Strapping of pinch tube to mount frame

ABSTRACT

In a jacketed lamp comprising an inner arc tube centrally supported within a vitreous outer envelope, the arc tube is attached to a mount frame by metal straps embracing its pinched ends. For a secure attachment, conventional practice has been to make the strapping tight by welding it together close to the arc tube. Improved strapping formed into an offset hairpin type clip provides a secure attachment without need of welds close to the arc tube. The strap on one side of the pinch is flat and that on the other has an offset of the thickness of the pinch with sharp bends into end portions lying next to and attached to the flat strap. This substantially eliminates possibility of the clip opening up by wedging action of the arc tube.

United States Patent 1191 Fitzgerald et al.

FRAME Filed:

STRAPPING OF PINCH TUBE TO MOUNT Inventors: Nelson Fitzgerald, Euclid, Edwin J.

Lohrey, Macedonia, both of Ohio Assignee: General Electric Company,

Schenectady, N.Y.

Dec. 27, 1972 Appl. No.: 318,934

US. Cl 313/25, 313/274, 313/276,

Int. (:1. 11011 1/02, H01 j 7/24, H01 j 61/52 Field of Search 313/25, 271, 274, 276,

References Cited UNITED STATES PATENTS Primary Examiner-Archie R. Borchelt Assistant Examiner-Saxfield Chatmon, Jr.

Attorney, Agent, or FirmErnest W. Legree; Lawrence R. Kempton; Frank L. Neuhauser 57 ABSTRACT In a jacketed lamp comprising an inner arc tube centrally supported within a vitreous outer envelope, the arc tube is attached to a mount frame by metal straps embracing its pinched ends. For a secure attachment, conventional practice has been to make the strapping tight by welding it together close to the arc tube. lmproved strapping formed into an offset hairpin type clip provides a secure attachment without need of welds close to the arc tube. The strap on one side of the pinch is flat and that on the other has an offset of the thickness of the pinch with sharp bends into end portions lying next to and attached to the flat strap. This substantially eliminates possibility of the clip opening up by wedging action of the arc tube.

9 Claims, 4 Drawing Figures STRAPPING OF PINCH TUBE TO MOUNT FRAME BACKGROUND OF THE INVENTION The invention relates to electric discharge lamps having an inner envelope mounted in a vitreous outer envelope or jacket, and more particularly to the attachment of the inner envelope or arc tube to the mount frame which supports it. It is of especial interest for high intensity lamps comprising a quartz arc tube with pinched ends enclosed within a glass outer jacket fitted with a screw base at one end. Common lamps of this kind include high pressure mercury vapor lamps utilizing a quartz'arc tube containing a filling of mercury, and high pressure metal halide lamps utilizing a quartz arc tube containing a filling of mercury and metal halides.

The outer envelope commonly has a neck portion closed by a re-entrant stem through which current inleads are sealed. The mount frame is generally a wire structure extending into the bulb from one of the inleads at the stem. It may comprise one or two side rods extending to the dome end where it is suitably anchored, for instance to an inwardly turned dimple. A]-

ternatively, the mount frame may be of so called side:

rodless construction wherein it is made in two parts, a lower part fastened to the inlead at the stem and an upper part anchored to the dome end, the arc tube serving as a bridge between parts. In either case, the arc tube must be attached to the mount frame and this is generally done by flexible metal .strips embracing the pinched or flattened ends of the tube, commonly referred to as the pinches. To achieve a secure attachment, conventional practice has been to make the strapping tight by welding it together close to the pinch. Since the arc tube pinches vary in size, the operator must exercise discretion each time a wcld is made. Thus a skilled operator is required, and the operation is not readily amenable to automation. Also the welds are relatively easily broken open by the wedging action of the pinches under stress resulting in a relatively high shrinkage rate.

SUMMARY OF THE INVENTION The object of our invention is to provide an improved strapping arrangement for attaching the arc tube to the mount, one which affords a secure fastening, which is not subject to wedging open, when is economical to manufacture and which lends itself to manual assembly or to automated assembly when desired.

According to our invention, the arc tube is attached to the mount frame by embracing its pinched ends in improved'offset hairpin-type clips. The clip is made of a flat strap on one side of the pinch, and another strap on the opposite side having an offset of the thickness and width of the pinch with sharp bends into end portions lying next to the flat strap. The strap with the offset has attachments to the flat strap at points beyond the sharp bends. Both sides may be formed from a continuous piece of strapping or metal ribbon by folding it back upon itself. The bend or fold then serves as one attachment and a single weld at the end removed from the fold serves as the other attachment and suffices for a secure closure. The offset configuration with sharp bends substantially eliminates possibility of the clip being opened up by the wedging action of the arc tube pinch. After the offset clips have been closed upon the pinches and spot-welded together, they are preferably attached by welding to the mount frame wires.

DESCRIPTION OF DRAWINGS FIG. 1 but to a larger scale and showing offset hairpin strapping according to the invention.

FIG. 4 is a greatly enlarged view of one edge of the pinch in FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawing and more particularly to FIG. 1, there is shown a high pressure mercury vapor lamp 1 embodying the invention in preferred form. It comprises vitreous envelope of jacket 2 of ellipsoidal shape having a neck 3 to the end of which is attached a screw type base 4. The neck 3 is closed by a reentrant stem Shaving a press portion 6 through which extend relatively stiff inlead wires 7, 8 connected to the contact surfaces of the base, namely the insulated center contact of eyelet 9 and the base shell 11.

Inner arc tube 12 is made of quartz and encloses a charge of mercury and an inert starting gas, suitably argon at a pressure of about 20 torr. It is provided at opposite ends with a pair of main discharge supporting electrodes l3, 14 to which connections are made by ribbon-type inleads sealed through the flattened ends of the tube. A fine tungsten wire 15 sealed into the arc tube at its lower end serves as an auxiliary starting electrode and is connected through a current limiting resistor 16 to inlead 7 by way of side rod 17. The side rod is welded to inlead 7 at the base end and extends to anchoring dimple 18 at the dome end of the envelope which it engages by a loop clip 19. The are tube is attached to the mount frame by clamping its flat ends 20 between strap clips 21, 22 which are welded to side rod 17. Outer envelope 2 may be coated internally with a phosphor layer 23 and may be either evacuated or filled with an inactive gas such as nitrogen.

The invention is more particularly concerned with the strap clips 21, 22 by which the arc tube is attached to mount frame 17. The conventional practice followed heretofore is illustrated by clip 21 in FIG. 2. The flat pinched end 20 of the tube is encompassed between a pair of thin flexible steel straps 25, 26. To assure tightness, the straps are bent and pulled together around the curved edges of the pinch and spot welded at 27, 28 as close the the edges of the pinch as practical. A weld too far out means a loose clamp whereas a weld too close to the pinch may result in fracture of the quartz. A loose clamp allowing lateral movement of the arc tube puts strains on the inleads and on the side welds thereto. Lateral movement of the arc tube must be prevented during manufacture and shipping, and also under operating condition. The stringency of these requirements has made the strip welding operation a relatively high shrinkage one.

When close welding is relied upon for tight strapping, the spot welds are relatively easily broken open under strain. This is so because the strap surfaces come together at a shallow angle and any force exerted by the pinch produces a wedgingjaction, as may readily be visualized in FIG. 2. The wedging action amplifies the forces tending to break apart the spot welds at 27 or 28.

An improved offset hairpin-type clip 21, 22 according to our invention is shown in FIG. 3. It may suitably be made of nickel-plated soft-tempered steel ribbon, 0.012 inch thick by 0.125 inch wide. It is preferably formed of a single piece providing a flat lower strap 30 folded back upon itself at 31 to make the upper strap having an offset portion 32 corresponding in height and width to the thickness and width of the quartz pinch. The lower corners at 33, 34 on either side of the offset must be formed with sharp bends leaving straight leg portions extending up to the midline of the offset, as shown at 35 in FIG. 4. By way of example, the pinch in a quartz arcttube for a 400 watt lamp will have a thickness of 3.3 millimeters and a width of 30 i 4 millimeters. In such case the sharp bends at 33, 34 are formed to a radius of 0.5 millimeter (0.02 inch) or less. The upper comers of the offset portion at 36, 37 need not be sharp bends and they are preferably rounded to the same curvature as the quartz pinch.

The width of the offset portion 33 must of course correspond to that of the particular pinch. We have found it preferable to partly'preform the hairpin clip with the fold at 31, the sharp bend at 33 and the rounded bend at 36. Thereafter the partly formed clip is slipped over the arc tube pinch and the rounded bend at 37 is mechanically formed around the pinch. When the bend at 37 is formed, a very slight upbowing may be formed into generally flat offset portion 32 overlying the pinch as illustrated, but this is not undesirable as it improves the resiliency of the attachment. A sharp end is made at 34 and upper and lower straps are spot welded together at 38. The closed clips are then spot welded at 39 to frame member 17, and also at 40 to frame member portion 17a in the case of lower clip 22. The function of these additional spot welds is to attach the clips to the mount frame; they are not necessary to hold the clips shut and there is no need to place them close to the edges of the quartz pinch.

Strain and drop tests on are tube mounts utilizing the offset hairpin-type clips illustrated in FIG. 3 have shown better resiliency and shock resistance and greater strength and resistance to breaking upon than the prior art strapping. There is substantially no tendency for spot weld 38 which holds the clip closed to break upon. This can be understood from consideration of FIG. 4 and the forces involved. Lateral force exerted by the quartz pinch on the clip, as represented by arrow 41, exerts a bending moment on the straight strap section 35 which tends to increase the curvature at the midpoint and at the sharp bend 34, as shown in dotted lines. As a result the force applied at the spot weld 38 is primarily in shear, and since there is no wedging action tending to break the spot weld open, it will hold securely. The additional spot welds used to attach the clip to the frame members 17, 17a, namely spot welds 39 and 40, are also effective to resist any shearing forces. Thus the invention provides a much stronger attachment of the arc tube to the mount frame than possible heretofore.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electric lamp comprising a vitreous envelope having a flat pinch at one end,

and a mount frame to which said envelope is secured by an offset hairpin type clip embracing said pinch and fastened to the mount frame,

said clip comprising a flat metal strap on one side of the pinch and another strap on the opposite side,

said other strap having an offset portion of the thickness and width of the pinch between leg portions having sharp bends into end portions lying next to said flat strap, said end portions being attached to said flat strap beyond said sharp bends.

2. A lamp as in claim 1 wherein there are straight leg portions extending from the midline of the pinch to the sharp bends into the end portions.

3. A lamp as in claim 1 wherein there are straight leg portions extending from the midline of the pinch to the sharp bends into the end portions, and the offset portion has rounded bends into the leg portions corresponding to the curvature of the pinch.

4. A lamp as in claim 1 wherein the clip is made of a single piece of metal ribbon folded back upon itself to provide said flat strap on one side of the pinch and said other strap on the opposite side into which said offset is formed.

5. A jacketed lamp comprising an outer vitreous envelope and an inner vitreous envelope having flat pinches at its ends,

said inner envelope being supported within said outer envelope by a mount frame to which it is secured by offset hair pin type clips embracing its pinches and fastened to the mount frame,

each clip comprising a single piece of metal ribbon folded back upon itself to provide a flat strap on one side of the pinch and another strap on the opposite side,

said other strap having an offset portion of the thickness and width of the pinch between leg portions having sharp bends into end portions lying next to said flat strap,

one end portion being attached to said flat strap at the fold and the other end portion being fastened to said flat strap beyond the sharp bend.

6. A lamp as in claim 5 wherein there are straight leg portions extending from the midline of the pinch to the 50 sharp bends into the end portions.

7. A lamp as in claim 5 wherein there are straight leg portions extending from the midline of the pinch to the sharp bends into the end portions, and the offset portion has rounded bends into the leg portions corre- 55 sponding to the curvature of the pinch.

8. A lamp as in claim 5 wherein said other end portion is fastened to said flat strap beyond the sharp bend by spot weld.

9. A lamp as in claim 5 wherein said clips are fas- 0 tened to the mount frame by spot welds through said end portions. 

1. An electric lamp comprising a vitreous envelope having a flat pinch at one end, and a mount frame to which said envelope is secured by an offset hairpin type clip embracing said pinch and fastened to the mount frame, said clip comprising a flat metal strap on one side of the pinch and another strap on the opposite side, said other strap having an offset portion of the Thickness and width of the pinch between leg portions having sharp bends into end portions lying next to said flat strap, said end portions being attached to said flat strap beyond said sharp bends.
 2. A lamp as in claim 1 wherein there are straight leg portions extending from the midline of the pinch to the sharp bends into the end portions.
 3. A lamp as in claim 1 wherein there are straight leg portions extending from the midline of the pinch to the sharp bends into the end portions, and the offset portion has rounded bends into the leg portions corresponding to the curvature of the pinch.
 4. A lamp as in claim 1 wherein the clip is made of a single piece of metal ribbon folded back upon itself to provide said flat strap on one side of the pinch and said other strap on the opposite side into which said offset is formed.
 5. A jacketed lamp comprising an outer vitreous envelope and an inner vitreous envelope having flat pinches at its ends, said inner envelope being supported within said outer envelope by a mount frame to which it is secured by offset hairpin type clips embracing its pinches and fastened to the mount frame, each clip comprising a single piece of metal ribbon folded back upon itself to provide a flat strap on one side of the pinch and another strap on the opposite side, said other strap having an offset portion of the thickness and width of the pinch between leg portions having sharp bends into end portions lying next to said flat strap, one end portion being attached to said flat strap at the fold and the other end portion being fastened to said flat strap beyond the sharp bend.
 6. A lamp as in claim 5 wherein there are straight leg portions extending from the midline of the pinch to the sharp bends into the end portions.
 7. A lamp as in claim 5 wherein there are straight leg portions extending from the midline of the pinch to the sharp bends into the end portions, and the offset portion has rounded bends into the leg portions corresponding to the curvature of the pinch.
 8. A lamp as in claim 5 wherein said other end portion is fastened to said flat strap beyond the sharp bend by spot weld.
 9. A lamp as in claim 5 wherein said clips are fastened to the mount frame by spot welds through said end portions. 